It is written in Flash I’m afraid, so if you are on iOS you’ll just have to look at the screenshot and imagine the moving planets. Perhaps I will write an HTML5 version using D3.js when I get a chance…

If your tastes are more retro, check out orrery in the marvellous ZX Spectrum Astronomy, including the whole 24-line BASIC program!

It is a great reminder of what you can do with a low-resolution display and a few tens of lines of code. Here is another example showing different trajectories.

Launch Phase Upon completion of this chapter you will be able to describe the role launch sites play in total launch energy, state the characteristics of various launch vehicles, and list factors contributing to determination of launch windows. You will be able to describe how the launch day of the year and hour of the day affect interplanetary launch energy and list the major factors involved in preparations for launch.

Or how about this…?

Interplanetary Trajectories Upon completion of this chapter you will be able to describe the use of Hohmann transfer orbits in general terms and how spacecraft use them for interplanetary travel. You will be able to describe the general concept of exchanging angular momentum between planets and spacecraft to achieve gravity assist trajectories.

If so, you need to read the fabulous Basics of Spaceflight by Dave Doody, a JPL engineer. You can browse it online, but a free PDF version is also available which has much nicer formatting.

It is very clearly written and has a broad scope, covering all aspects of space travel and exploration.

I love the fact that the spacecraft’s position was indicated by a clockwork globe.

I really want to know more about the “ingenious Vzor periscope”. What a great name.

The Vostok and Voskhod spacecraft, like the U.S. Mercury, could not perform orbital maneuvers – they could only be translated around their axes. The main engine was used only at the end of the mission for the reentry braking maneuver. Instrumentation on the Vostoks was rudimentary in the extreme. There were no gyros and no eight-ball for maneuvring as on the Gemini. The reentry maneuver was normally handled automatically by radio command. Spacecraft attitude in relation to the local motion along the orbit was determined by sun sensors, infrared horizon sensors and ion gauges, which could detect the spacecraft’s direction of motion by the greater velocity of ions impacting the spacecraft in the direction of motion.

The cosmonaut could, however, take control of the spacecraft and manually reenter. This was done by using the ingenious Vzor periscope device mounted on the floor of the cabin. This had a central view and eight ports arranged in a circle around the center. When the spacecraft was perfectly centered in respect to the horizon, all eight of the ports would be lit up. Alignment along the orbit was judged by getting lines on the main scope to be aligned with the landscape flowing by below. In this way, the spacecraft could be oriented correctly for the reentry maneuver. To decide when to reenter, the cosmonaut had a little clockwork globe that showed current position over the earth. By pushing a button to the right of the globe, it would be advanced to the landing position assuming a standard reentry at that moment. This manual system would obviously only be used during daylight portions of the orbit. At night the dark mass of the earth could not have been lined up with the optical Vzor device. The automatic system would work day or night.